Growth and survival of Arcto-Norwegian and Norwegian coastal cod larvae (Gadus morhua L.) reared together in mesocosms under different light regimes
Abstract :
To evaluate genetic differences in growth and
survival potential as a function of light regime, cod larvae from two stocks
(CC: coastal cod and AC: Arcto-Norwegian cod, spawning at latitudes of 60°N
and 69°N respectively) were co-reared in mesocosms. The experiment was
carried out with two artificially illuminated light regimes, corresponding
to the natural photoperiod at peak spawning of the respective stocks (CC:
7–8 h distinct dark period, AC: ‘mid-night sun’ as continuous
light with 2–3 h reduced light intensity). One additional regime with
ambient natural light analogous to 60°N was used. At termination on day 36
post-hatch, larvae of the co-reared stocks were distinguished from each
other by a genetic marker in the CC stock. Stock-specific differences in
growth rate and survival were indicated, with CC larvae growing and
surviving better than AC larvae. This is in agreement with earlier
comparisons of larval growth in these stocks. The 69°N light regime did not
enhance growth for any of the two stocks. However, natural light greatly
increased growth rate of both stocks, indicating important mechanisms in
regulation of larval feeding relative to light quality or intensity. The
results may be important for choice of stock and illumination in intensive
aquaculture of this species.
(Institute of Marine Research, Austevoll Aquaculture
Research Station, N-5392 Storebø, Norway)